An antenna is an electrical device designed to convert electrical signals into radio waves or electromagnetic (EM) waves, and vice versa, for a given frequency band. Antennas are widely used in systems that utilize EM waves for carrying signals, such as cell phones, radar, satellite communication, as well as other devices such as wireless computer networks, wireless wearable devices and radiofrequency identification (RFID) tags on merchandise. To satisfy a range of device working frequencies and applications, a large number of different types of antenna have been developed and commercialized since 1895. Antennas are typically constructed from conductive wires that are electrically connected to a receiver or transmitter by a transmission line. When an oscillating current signal is fed into the wire, an oscillating magnetic field is created around the antenna. In addition, the oscillating magnetic field creates an oscillating electric field, and thus a time-varying field radiates away from the antenna into space. The frequency of the radiation signal may be inversely proportional to the size of the antenna, such that smaller devices lead to higher working frequencies.
Almost all the current antenna designs focus on frequencies below the terahertz (THz, 1012 Hz) band, which may be defined to extend from 0.1 THz to 10 THz. The THz band is considered to be an important part of the EM spectrum as it includes frequencies with numerous potential physical and chemical applications. However, for a long time, due to the unavailability of powerful THz sources, transmission lines, detectors and other components, this band remained untapped and has become known as the “terahertz gap.” During the past decade, various THz components and instruments have been developed to bridge this gap.
There is demand for a high performance THz antenna in applications where THz EM energy needs to be radiated or received. One example is the future high data rate communication system. A data rate of more than 100 Gbps for outdoor communication and more than 40-100 Gbps for indoor communication can be obtained by increasing the operating frequency to the THz band, so that even with a narrow bandwidth, the data rate may be high enough for target applications. Unfortunately, the atmospheric path loss at the THz band is significant, and thus high-power sources, efficient detectors and a high gain THz antenna are being developed to overcome the problem. Due to the limitations of current power sources and detectors, however, high gain THz antennas may need to play a more important role in realizing advanced wireless systems.